This application claims the priority of Korean Patent Application No. 2003-38375, filed on Jun. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an Ethernet switch, and apparatus and method for expanding a port, and more particularly, to an Ethernet switch, and apparatus and method for expanding a single physical port to a plurality of logical ports.
2. Description of the Related Art
A conventional Ethernet switch includes a filter/transmission logic, a learning logic, and an address table. The filter/transmission logic checks a destination address of a received frame and compares the destination address with entries of the address table. When the destination address of the received frame exists in the address table and an output port corresponding to the destination address is not a port through which the frame is received, the filter/transmission logic transmits the frame to the port of the destination. When the output port corresponding to the destination address is the port through which the frame is received, the filter/transmission logic performs filtering by discarding the frame. When the address table does not include any information on the destination address, the filter/transmission logic floods the frame to all ports.
The learning logic collects a source address of the received frame and input port information and updates the address table. Each entry of the address table includes a media access control (MAC) address of a host and a port that has received a frame the most lately. The address table is updated by the learning logic and is used by the filter/transmission logic to determine on the transmission of a received frame. Each entry of the address table has a timer which indicates a time lapse used to determine when a MAC address will be discarded. Because the size of the address table within a switch is limited, the number of MAC addresses, i.e., hosts, that can be allocated to a single Local Area Network (LAN) switch is restricted.
A conventional high-speed switch does not transmit a received frame through a port through which the frame has been received. When a plurality of low-speed ports are connected to the conventional high-speed switch through an apparatus simply performing multiplexing/demultiplexing, a frame cannot be transmitted between the low-speed ports. Accordingly, when a plurality of low-speed ports are connected to a high-speed switch, a low-speed switch or a bridge for transmitting frames between the low-speed ports is required to be provided between the high-speed switch and the plurality of low-speed ports.
FIG. 1A illustrates downstream traffic flow in a conventional Ethernet Passive Optical Network (EPON). The conventional EPON includes an optical link terminal (OLT) 100, a plurality of optical network units (ONUs) 120,122, and 124, and a splitter/coupler.
Data of a frame is formed in a variable-length packet and is transmitted (i.e., broadcast) from the OLT 100 to all of the ONUs 120, 122, and 124. Packets 110, 112, and 114 include information on the respective ONUs 120, 122, and 124 to which they are supposed to be transmitted, respectively, in a logical link Identification (LLID) field located at the front portion of a frame, separately from a MAC address. When data reaches the ONUs 120, 122, and 124, each of the ONUs 120, 122, and 124 receives a packet designated to it and discards the other packets.
FIG. 1B illustrates upstream traffic flow in a conventional EPON. In FIG. 1B, upstream traffic from ONUs 170, 172, and 174 to an OLT 150 is managed using Time Division Multiplexing (TDM). The ONUs 170, 172, and 174 transmit upstream data 160, 162, and 164, respectively, in time slots which the OLT 150 allocates to the ONUs 170, 172, and 174, respectively, using TDM so that the data 160, 162, and 164 are prevented from colliding. Like a packet in downstream traffic, a packet in upstream traffic also includes an LLID, which indicates a source ONU from which the packet is forwarded.
Frames from ONUs are transmitted to an OLT and frames from the OLT are transmitted to the ONUs through a single physical line provided between the OLT and a splitter/coupler. A downstream signal is transmitted to all of the ONUs, and an upstream signal from a certain ONU is transmitted to only the OLT without collision. To implement a bridge function for virtual, logical ports distinguished by LLIDs, the OLT is required to identify a virtual port connected to a single physical EPON line and function as a bridge. However, a conventional high-speed switch does not support virtual port identifiers, and therefore, it cannot transmit a frame through a physical port through which the frame has been received. In other words, when a conventional EPON is connected to a conventional high-speed switch, frames cannot be transmitted between ONUs.